Minimally invasive transforaminal lumbar interbody fusion

ABSTRACT

This disclosure presents a MITLIF procedure. The procedure uses a single incision on one side and pedicle screws are placed on that side and through the same incision a facet screw is placed on the opposite side using a series of jigs, and, for example, the hole cutter, drill, guide shaft and screw driver described herein.

CROSS REFERENCE TO RELATED APPLICATION

This application claims priority to U.S. Provisional Application No.62/739,205, filed Sep. 29, 2019, the disclosure of which is incorporatedherein by reference.

BACKGROUND

There are numerous research papers documenting the advantages ofminimally invasive surgery. Such advantages include less blood loss,shorter operating duration, shorter hospitals stay, and less musculardamage.

Segmental spinal fusions which stabilize two or more adjacent segmentsof the spine are performed for painful degenerative disc disease,recurrent disc herniations, spinal stenosis, spondylolysis andspondylolisthesis. Over the past several decades a wide variety offusion techniques and instrumentation have evolved.

Efforts have been made to extend minimally invasive surgery techniquesto spinal fusion and repair, including transforaminal lumbar interbodyfusions (minimally invasive transforaminal lumbar interbody fusion(MITLIF)). Such techniques have demonstrated equally good long termoutcomes compared to non-MITLIF procedures.

SUMMARY

The disclosure provides a method of minimally invasive transforaminallumbar interbody fusion (MITLIF) comprising: drilling a hole in aspinous process using a hole cutter; inserting a guide shaft into thehole of the spinous process down to a facet joint; inserting a drillthrough the inner diameter of the drill guide; drilling a hole in thefacet joint; inserting a facet screw and screwdriver though the innerdiameter of the drill guide; and seating the screw into the facet joint.In one embodiment, the method further comprises placing pedicle screwson the opposite side of the spinous process. In another embodiment, anaccess for placement of the pedicle and facet screws is the same accessfor both.

The disclosure also provides a surgical system for carrying out themethod of the invention. In one embodiment, the surgical systemcomprises a surgical guide shaft device comprising a first end, a secondend, a lumen extending and open from the first end to the second end andhaving and internal diameter “D” and an external diameter “X”, whereinthe second end comprises a traction system comprising one or moreprong(s) and traction feet; a drill bit comprising a shaft having one ormore stabilization collars a drill tip at one end of the drill bitwherein the one or more stabilization collars having a diameter smallerthan the diameter D of the guide shaft such that the collars can bemoved along the length of the shaft while maintaining the shaft of thedrill substantially centered in the lumen of the guide shaft; and ascrew-driver comprising a shaft, a tip for engaging a screw and one ormore stabilization collars, wherein the one or more stabilizationcollars have a diameter smaller than the diameter D of the guide shaftsuch that the collars can be moved along the length of the shaft whilemaintaining the shaft of the screw driver substantially centered in thelumen of the guide shaft.

The disclosure also provides a surgical guide shaft device for minimallyinvasive transforaminal lumbar interbody fusion comprising a tube havingat least one wall, a first end and second end, the tube having adiameter “D”, wherein the second end comprises a traction system havingat least one prong and a plurality of traction feet. In one embodiment,the at least one prong comprises at least two prongs. In a furtherembodiment, the at least two prongs are about 2 mm long and about0.5-1.5 mm in diameter with a tapered/pointed end extending from the atleast one wall and parallel with the length dimension of the tube. Inanother embodiment, the guide shaft device further comprises a handleaffixed to the outside of the tube suitable for grasping andmanipulation by a surgeon.

The disclosure also provides a surgical drill bit comprising a shafthaving a first end and second end, a drill head at the first end of theshaft, one or more stabilization collars, wherein the stabilizationcollars have a diameter greater than the diameter of the shaft andlocated between the first end and second end of the shaft. In oneembodiment, wherein the one or more stabilization collars comprises onestabilization collar and wherein the length of the collar is about 10%to about 90% the length of the shaft. In another embodiment, the one ormore stabilization collars comprise two stabilization collars andwherein each of the stabilization collars are about 2% to about 30% thelength of the shaft and wherein the stabilization collars are separatedfrom one another along the length of the shaft.

The disclosure also provides a surgical screw driver comprising a shafthaving a first end and second end, a head at the first end of the shaftfor engaging a screw, one or more stabilization collars, wherein thestabilization collars have a diameter greater than the diameter of theshaft and located between the first end and second end of the shaft. Inone embodiment, the one or more stabilization collars comprises onestabilization collar and wherein the length of the collar is about 10%to about 90% the length of the shaft. In another embodiment, the one ormore stabilization collars comprise two stabilization collars andwherein each of the stabilization collars are about 2% to about 30% thelength of the shaft and wherein the stabilization collars are separatedfrom one another along the length of the shaft.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 provides a schematic of a guide shaft of the disclosure.

FIG. 2A-B provide schematics of the traction end of the guide shaft infurther detail.

FIG. 3 provides a further schematic of a guide shaft of the disclosureincluding a handle for guiding the guide shaft.

FIG. 4 provides a schematic of a hole cutter.

FIG. 5 provides a diagram of a drill of the disclosure.

FIG. 6 provides a diagram of a screw-driver of the disclosure.

FIG. 7 depicts an example of the system wherein the drill (including ascrew) is guided through a guide shaft.

FIG. 8A is a general depiction of a spinal vertebrae.

FIG. 8B depicts the process wherein the guide shaft is inserted througha hole in the spinal process cut by the hole cutter to reach thepedicle/transverse process opposite an incision site.

FIGS. 9 and 10 depict the use, surgical process using the devices ofFIGS. 1-7 in the methods of the disclosure.

DETAILED DESCRIPTION

As used herein and in the appended claims, the singular forms “a,” “an,”and “the” include plural referents unless the context clearly dictatesotherwise. Thus, for example, reference to a “a screw” includes aplurality of screws and reference to “the pedicle” includes reference toone or more pedicles and equivalents thereof known to those skilled inthe art, and so forth.

Unless defined otherwise, all technical and scientific terms used hereinhave the same meaning as commonly understood to one of ordinary skill inthe art to which this disclosure belongs. Although any methods andreagents similar or equivalent to those described herein can be used inthe practice of the disclosed methods and compositions, the exemplarymethods and materials are now described.

All publications mentioned herein are incorporated herein by referencein full for the purpose of describing and disclosing the methodologies,which are described in the publications, which might be used inconnection with the description herein. The publications discussed aboveand throughout the text are provided solely for their disclosure priorto the filing date of the present application. Nothing herein is to beconstrued as an admission that the inventors are not entitled toantedate such disclosure by virtue of prior disclosure. Moreover, withrespect to any term that is presented in one or more publications thatis similar to, or identical with, a term that has been expressly definedin this disclosure, the definition of the term as expressly provided inthis disclosure will control in all respects.

Also, the use of “and” means “and/or” unless stated otherwise.Similarly, “comprise,” “comprises,” “comprising” “include,” “includes,”and “including” are interchangeable and not intended to be limiting.

It is to be further understood that where descriptions of variousembodiments use the term “comprising,” those skilled in the art wouldunderstand that in some specific instances, an embodiment can bealternatively described using language “consisting essentially of” or“consisting of.”

The term “about” as used herein can allow for a degree of variability ina value or range, for example, within 10%, within 5%, or within 1% of astated value or of a stated limit of a range. When a range or a list ofsequential values is given, unless otherwise specified any value withinthe range or any value between the given sequential values is alsodisclosed.

One attempt to simplify the transforaminal lumbar interbody fusion(TLIF) procedure has been to use unilateral fixation. The results havebeen controversial. Some research papers have shown that unilateralfixation has equal outcome compared to bilateral fixation. There areother papers that showed that unilateral fixation has a higher incidenceof displaced spacers than bilateral fixation. Bilateral fixation isnormally performed by making an incision on both sides of the vertebrae,placing a K-wire into the pedicle, followed by placing the pedicle screwover the K-wire. A series of jigs are then used for the placement of therod and set screws.

As early as ten years ago the biomechanical study by Slucky et al.(Spine J, 6:78-85, 2006) showed that pedicle screws on one side and thefacet screws on the other side had equal strength compared to bilateralpedicle screws. They noted that it would be desirable if a method ofplacing this type of fixation could be done through a minimally invasiveapproach. A clinical series comparing bilateral pedicle screws fixationto pedicle screws on one side and the facet screws on the other sideshowed that the latter was equally effective on a clinical bases.

Complications of pedicle screw placement include duration of procedure,significant tissue dissection and muscle retraction, misplaced screwswith neural and/or vascular injury, excessive blood loss, need fortransfusions, prolonged recovery, incomplete return to work, excessrigidity leading to adjacent segmental disease requiring further fusionsand re-operations. Further advances of pedicle screw fixation includingminimally invasive and image-guided technology, and the development offlexible rods have imperfectly addressed some but not all of theseissues. Transfacet screws and similar embodiments entail the use ofshort or long screws which provide static facet alignment without motioncalibration.

This disclosure presents a prospective series of MITLIF procedures. Whatmakes this procedure unique is that a single incision is used on oneside and pedicle screws are placed on that side and through the sameincision a facet screw is placed on the opposite side. The disclosureprovides both the methodology for performing this MITLIF as well asdevices useful for performing the method.

Turning to FIG. 1, the figure depicts a guide shaft 10 comprising afirst end 12, a second end 14, a lumen 19 having and internal diameter“D” and an external diameter “X”. The guide shaft 10 can be made of anyresilient sterilizable and biocompatible material (e.g., surgicalsteel). Second end 14 comprises a traction system comprising prong(s) 18and traction feet 16.

FIGS. 2A-B depict second end 14 in further detail. FIG. 2B depictssecond end 14 having two prongs 18. In one embodiment, the prongs 18 are1-3 mm long (e.g., about 2 mm long) and have a diameter of about 0.5-1.5mm (e.g., about 1 mm).

FIG. 3 shows guide shaft 10 further including a handle 20 for usedduring the procedure to hold an manipulate the guide shaft 10 during theprocedure and placement through a spinal process.

FIG. 4 shows a hole cutter 30. Hole cutter 30 includes a shaft 32, head35 comprising teeth 37 used for cutting a hole in a spinal process. Thehead 35 has a diameter “X” that is equal to or slightly larger (e.g.,micrometers to a millimeter larger) than the outside diameter of theguide shaft 10. The diameter of the head 35 should be large enough todrill a hole in a spinal process such that the guide shaft 10 can beinserted through the hole. The hole cutter typically comprise a tungstencarbide, stainless steel or other suitable surgical drill material.

FIG. 5 is a drawing of a drill used in the surgical system of thedisclosure. The drill 50 includes a shaft 52 having one or morestabilization collars 54 a and 54 b that can be integral with the shaftor may be distinct in the form of bearing collars and the like. If onestabilization collar is present, the length of the collar is sufficientthat the shaft remains substantially centered in the lumen 19 of theguide shaft 10 during use. The drill 50 includes a drill tip 56 at oneend of the drill 50. The stabilization collars 54 a and 54 b have adiameter “D” which is slightly less (e.g., micrometers less) than theinternal diameter of the guide shaft 10. The diameter of thestabilization collars 54 a and 54 b should be a diameter that allows thestabilization collars 54 a and 54 b to suitably slide into and out ofthe lumen 19 of the guide shaft 10 while reducing the lateral movementwithin the lumen 19, such that during operation of the drill the drillis held in a substantially steady position (see also FIG. 7).

FIG. 6 depicts a screw-driver of the disclosure. Screw-driver 60includes a shaft 62, a tip 66 for engaging a screw and stabilizationcollars 64 a and 64 b. The stabilization collars 64 a and 64 b have adiameter which is slightly less (e.g., micrometers less) than theinternal diameter of the guide shaft 10. The diameter of thestabilization collars 64 a and 64 b should be a diameter that allows thestabilization collars 64 a and 64 b to slideably inserted into and outof the lumen 19 of the guide shaft 10 while reducing the lateralmovement within the lumen 19, such that during operation of thescrew-driver the screw-driver is held in a substantially steady position(see also FIG. 7, which depicts a screw 70 engaged with the screw-driver60).

FIG. 8A depicts a general structure of a vertebrae, while FIG. 8Bdepicts the insertion of a guide shaft 10 of the disclosure through thespinous process.

Turning to FIG. 9, the figure depicts the use of the hole cutter inboring a hole in the spinous process of a vertebrae. The hole cuttercomprises a diameter that is smaller than the average diameter size ofthe average human spinous process. In addition, the hole cutter is equalto or slightly larger than the diameter of the external diameter of theguide shaft 10. The guide shaft 10 comprises an internal diameter equalto, or slightly larger (e.g., um to less than about 1 mm larger than thediameter of the drill and screw driver. Thus, once the guide shaft 10 isaligned then the drill and screw driver are aligned.

As shows in FIG. 9 an initial hole is made in the spinous process. Theguide shaft 10 is inserted down to the facet joint (FIG. 10). Alignmentcan be confirmed with an oblique X-ray or through computer guidance.

The drill is then guided to the facet through the interior of the guideshaft 10. A drill hole is then made and a facet screw (e.g., FACETFIXX®, Nexxt Spine) is inserted using the screw driver 60. The screwdriver 60 is detached from the screw 70. Pedicle screws are placed(e.g., with computer guidance or X-ray) and a rod and set screws areinserted.

In use the general process includes making a vertical line directly overthe midline and a 2^(nd) vertical line over the pedicle using C-armcontrol. An incision is made over the marked area from pedicle topedicle. The facet joint below and above is then exposed. A laminectomyis then carried out working toward the head to the level of the disc.The dura is retracted medially and a discectomy is carried out. The discis prepared for fusion, bone graft is packed into the disc spacefollowed by an appropriate-sized spacer.

On the incision side, pedicle screw placement is inserted using X-ray,K-wire and cannulated screw (this can be performed by a computerizedguided system). A hole is made in the spinous process using the holecutter 30. The guide shaft 10 is then inserted into the hole of thespinous process down to the facet joint. Computer guidance or obliqueX-ray can be used to adjust and direct the guide shaft 10 accordingly. Adrill hole is then made in the facet joint. The drill hole is aligneddue to the inside diameter of the guide shaft 10. With the guide shaft10 in place, a facet screw (e.g., FACET FIXX® TransLaminar Screw) isinserted and again there is alignment from the guide shaft 10. A mark onthe screw driver will provide guidance as to when the screw is fullyseated. The screwdriver 60 and guide shaft 10 are removed. The area isthen decorticated and then packed with graft followed by the rod and setscrews.

EXAMPLES

Study Design: A prospective study was carried out on fifty-nine informedparticipants. The study population included all patients with mild tomoderate, central and peripheral stenosis. Pain intensity, was recordedusing a visual analogue scale (VAS). The participants were in the 19 to75 age range, the mean age was 58.7 years. The group consisted of 34male and 25 female patients.

The follow up was performed for several months to years. The originalseries consisted of 62 patients but 3 were excluded due to lack offollow up. The information obtained in the study consisted of surgicaltime; hospitalization time; blood loss and documentation of union of thefusion site. All complications were documented including displacement ofthe spacer, wound healing or infection, and non-union.

The fusion was determined by X-Rays and CAT scan using Bridewellcriteria. All cases had X-ray at 2 weeks, 3 months, 6 months, and 1 yearpost operation. Cases were considered a union if bone bridging acrossthe disc was observed on X-ray or CT scan, there was no lucency aroundthe fixation, there was no lucent line extending across the fusion mass.If there was a question of bone bridging on X-ray then a CAT scan wasdone. A total of 20 CAT scans were done.

The majority of the procedures were carried out at the L4-LS (n=44)level and were single level procedures, however one two level procedurewas carried out and a smaller number of procedures were carried out atdifferent level beside L4-LS: L5-S1 (n=10), L3-L4 (n=2), L2-L3 (n=1).

There were four cases of documented non-union for a total percentage of6.7% and they were all treated by anterior interbody fixation withhealing. In one of these the spacer had migrated to the bone and was notable to be removed but did not appear to be a problem with the fusion.

During the TLIF procedure two types of spacers were used. There were 20titanium spacers and 39 PEEK spacers. None of the titanium spacersdisplaced but they have a tendency to migrate and subside into the bone.This has also been noticed in other publications.

There was one case of deep infection, which occurred 3 months after thesurgery. This patient has been admitted to a nursing home due to urinarytract infection, which seeded the surgical site. The infectioncompletely resolved with a long term course of antibiotic while,treating the urinary infection. The bone disruption was not discovereduntil later date and it was treated by an anterior interbody fusion. Atthat time there was no evidence of acute infection but only extensivebone destruction. This went on to heal following the anterior interbodyfusion.

The blood loss ranged from 30 cc to 250 cc and averaged 152.6 cc.Surgery time ranged from 1 hour 40 minutes to 3 hours 10 minutes,averaging 2 hours and 3 minutes.

It has been documented that MITLIF has many advantages ranging from lessblood loss, less time in the hospital, to reduced post-operative pain.The technique that has just been described allows bilateral internalfixation through a single minimally invasive incision.

The fusion rate in a literature review of MITLIF by Goldstein revealed afusion ranging from 0% to 16.7% averaging 3.2%. The non-union rate forthis procedure is relatively high. A further research group had anon-union rate of 3.4%. This is attributed to improved technique asexperience was obtained with this procedure.

There was no loosening of the facet screw unless there was alsoloosening of the pedicle screws and a non-union.

This procedure requires a moderate amount of muscle that needs to beremoved. The removed muscle it is estimated to be in the order of threeto four cubic centimeter. This is a relatively small amount of the crosssection of the multifidus muscle. The facial attachments to the spinousprocesses remains intact. Furthermore this particular level is beingfused. Clinically there does not appear to be any problem as result ofremoving this amount of muscle.

All cases were done with a computer guidance system (Brain Lab). Thisexpedites the procedure and makes it easier. However the same procedurecan be done using X-ray. A single oblique view is all that is necessaryfor placement of the facet screw. Once the screw is placed,anterior-posterior and lateral X-Ray can be made.

Because the facet screw is placed dorsal and distal to the nerve rootthere is minimal chance of nerve irritation during fixation. There wasno clinical evidence of nerve root irritation in this series.

This series would tend to confirm that a unilateral decompression isadequate for moderate foramina and central stenosis. There are 2 factorsthat could have helped the decompression: (1) the side selected fordecompression was the side with the most stenosis, and (2) in additionto the unilateral laminar and foramina direct decompression, the discdecompression would help both sides.

Since the exposure is medial to the facet joint, there is no exposure ofthe transverse processes for placement of graft. Some graft can beplaced on the remaining superior facet joint below and the lower part ofthe superior facet joint above. Most of the fusion potential is from theintra discal graft.

What is claimed is:
 1. A method of minimally invasive transforaminallumbar interbody fusion (MITLIF) comprising: drilling a hole in aspinous process using a hole cutter; inserting a guide shaft into thehole of the spinous process down to a facet joint, wherein the guideshaft comprises a lumen defining an inner diameter of the guide shaft;inserting a drill through the lumen of the guide shaft, the drill havinga shaft and at least one stabilization collar moving within the lumen ofthe guide shaft that maintains the shaft of the drill substantiallycentered in the lumen of the guide shaft; drilling a hole in the facetjoint with the drill; inserting a facet screw and screwdriver though theinner diameter of the guide shaft; and inserting the facet screw intothe facet joint with a screw-driver comprising at least onestabilization collars moving within the lumen of the guide shaft thatmaintains the shaft of the screw driver substantially centered in thelumen of the guide shaft.
 2. The method of claim 1, further comprisingplacing pedicle screws on a side of the spinous process opposite to aside that the facet screw was placed.
 3. The method of claim 2, whereinan access for placement of the pedicle and facet screws is the sameaccess for both.